There are plenty of free utilities to unzip zip files, and most operating systems can do this for you anyway.

The templates are there to show you the dimensions of each piece of artwork, and where the edges and borders lie. You load each into some drawing or photo-eding software, set it as background, then create the layers of your design above it. Alternatively, you can set it as the top layer and set it to 50% opacity so you can see the positioning of your layers through it. If all of this is mumbo-jumbo to you, you will first need to learn how to use drawing or photo-editing software. There are free packages that do this Photo-editing: GIMP, etc. Drawing: Irfanview, etc.